1. Field of the Invention
The present invention relates to ram type blowout preventers which are hydraulically activated to seal about a pipe string of an oil or gas well to confine and control the pressure therein. More particularly the invention relates to replaceable wear inserts which seal about the pipe and which may be replaced when worn, thus saving the ram for further use. Most particularly the invention relates to replaceable wear inserts for use with heavy rubber ram packers having improved elastic flow characteristics.
2. Related Art
There are many styles of ram type blowout preventers available. One style, as illustrated in U.S. Pat. No. 4,825,948 issued to Carnahan comprises a ram body with a remotely replaceable shoe assembly, the sealing surface being integral with the shoe. The patent discloses ram shoes that are remotely removable and replaceable and includes a good background discussion of blowout preventers in general.
Generally a wear insert is placed in a cutout on the face of a ram front body. The body of such a ram is usually of a heavy rubber material and the wear insert of an elastomeric material such as TEFLON or high molecular weight polyethylene. The wear insert may be retained within the ram packer by radial fasteners such as screws.
U.S. Pat. No. 4,398,729 issued to Bishop, et al. has a ram body with a ram front packing including a backing portion of elastomeric material and a replaceable insert portion also of an elastomeric material having a detent on the outer surface of the seal insert, such as, a pair of securing members extending from the sides of the wear insert to prevent rotation. At column 4 at lines 22–27, the patent discloses that the shape of the insert that fits in the ram packer can have any configuration, such as a rectangular or multi-sided, in addition to the semicircular shape shown, so long as the seal member of the packer corresponds with a detent on the insert seal. The securing members and the corresponding notches in the ram packer, serve to prevent lateral rotation in and horizontal displacement out of the detent when the packer is drawn back from the pipe string. Thus, the configuration of the insert as either rectangular or multi-sided with a projection thereon is old and well known in the art from U.S. Pat. No. 4,541,639.
The elastomer comprising the ram packer forms a reservoir, such that as the surface in contact with the rotating pipe is worn away, the elastomer reservoir in the ram packer supplies additional elastomer to pressure the insert into the depleted areas. The ability to obtain as long a useful life as possible for the wear insert, depends on the ability of the elastomer in the reservoir to have flow access throughout the entire ram packer.
It has been found that when the multi-sided wear inserts of the prior art, are used the shoulders, which form the rectangle and the multi-sided configuration come into contact or very near to contact with the back of the ram packer to form a blockage of the elastomer flow from the reservoir to areas requiring increased pressure. The inhibition of the elastomer flow hastens the failure of the wear insert seal with the pipe, requiring its premature replacement and resulting lost drilling time.
It is an advantage of the present invention that the present wear insert provides a pathway for elastomer flow through the ram packer even when the configured shoulders would otherwise be fully compressed against the back of the ram packer.